As is known in the art, one technique used to cool electrical components in electrical cabinets is with fans. The amount of airflow (and thus the cooling) through the cabinet is controlled by adjusting the speed of the fans in accordance with the temperature within the cabinet. The individual fan speed (RPM) is typically adjusted by varying the duty-cycle of a Pulse-Width-Modulated (PWM) control signal that is the control input signal to the fan (i.e., a desired fan speed). The actual fan speed (RPM) is monitored with a signal produced by a fan-mounted tachometer.
As is also known in the art, in some cabinets there is a plurality of temperature sensors disposed at various locations with in the cabinet. The PWM signal is generated by a system controller or system microcontroller that responds to the sensed temperatures. The system microcontroller may transmit the desired PWM signal (i.e., desired RPM) directly to the fans and the actual RPM signal produced by the tachometers may be fed directly to the system microcontroller. Thus, the fan unit has a pair of terminals, in addition to power terminal and ground terminal), one terminal for the desired fan speed in PWM from the system microcontroller the other terminal for actual fan speed from the tachometer.
As is also known in the art, there are a variety of different communication protocols used to communicate between devices and a microcontroller. One is Inter-Integrated Circuit (I2C), sometimes also referred to as, and hereinafter referred to as, two-wire interface (TWI)) where a pair of lines is provided; one line for data and one line for clock—these two in combination providing the information between the microcontroller and the device (in this case the fans) and another is UART which also has a pair of lines; one for transmitting data (Tx) to the device and the other for receiving data (Rx) from the device.